Affordances

Definition

When you look around a room, what do you see? You may say that you see chairs, tables, flooring, bookshelves, and walls. And at one level, perhaps you do. According to James J. Gibson's ecological theory of perception, at another level you see possibilities for action. These possibilities for action are termed affordances.

Analysis

The mantra of this approach is, as Gibson noted in 1979, that “perception is for doing.” We perceive the world not to create an accurate internal representation of an external reality as an end in itself. Rather, our [Page 19]perceptual systems have been tuned, over the course of evolution, to pick up information that is useful—ultimately, from an evolutionary perspective, useful to tasks that, in ancestral environments, would have enhanced survival and reproduction. To pick up that information, it is unnecessary to first create a big picture of the world inside of our head and then identify, within that picture, what we find useful. Rather, according to Gibson, information pertinent to useful action is perceived “directly.”

Gibson invented the term affordance to refer to the features of objects that are useful to action. A meaning of the term afford is “to make available” or “to provide.” An affordance is a feature that makes available a course of action. A passageway affords movement through space. A doorknob affords grasping. A ripe apple affords eating.

Affordances, Gibson argued, really do exist in the world. The world is there to be navigated though, climbed, consumed, and it contains dangers that must be avoided as well. Features of the world that facilitate effective action are directly perceived and acted upon. Gibson's approach can be contrasted with a different view of perception—the idea that we first construct a view of the world—create a “picture” of the world in our heads—and then identify within that picture what is useful. Gibson argued that much useful information is embodied in the environment. Value and utility for organisms exist in the world. Our perceptual senses have been tuned to “pick up” this information.

Because features have different affordances for different organisms, different organisms will see the world differently at a fundamental level. Indeed, a good way to appreciate what Gibson meant by an affordance is to imagine the world through two different sets of eyes. For you, a “stair” affords climbing. If a stair riser's height is less than 88% of an individual's lower leg length, the stair can be climbed in a bipedal fashion. If its height is greater than that amount, it cannot. A stair of appropriate height affords climbing, and we pick up information about climbability. That affordance exists in the world for us. For a house cat, this same stair also affords climbing—though of course the cat will not climb it with two feet, as we will. A house cat will also pick up the feature “climbable” in a set of stairs.

Now consider a table. For you, a table has an affordance to set things upon. It has an affordance to sit at—and thereby to eat at and work at. For a cat, a table does not have these affordances. Instead, a table has an affordance to be jumped upon and thereby explored. You do not typically perceive a table as something to be jumped upon to be explored. According to Gibson, then, you and a cat perceive a table in fundamentally different ways. You look at a table and see “something to set things upon.” A cat looks at a table and sees “something to be jumped upon.”

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